Transducer positioner in disk files

ABSTRACT

The transducer or transducers are mounted to the bottom of a U-frame carrying a coil between the legs; the coil is slipped onto and runs over a bar, facing two permanent magnets. One leg of the U-frame is suspended on leaf springs, being connected also to a base, so that the frame moves strictly linearly without lateral displacement. A similar spring mount may be connected to the other leg of the U-frame. The springs may have a U-configuration or an E-configuration.

BACKGROUND OF THE INVENTION

The present invention relates to actuators and positioners fortransducers in disk files.

Disk files are well established fast-access-memory units in the computerart. These disk files include large or small disks of a hard or flexibleconfiguration. Magnetic transducers are to be positioned in relation tothe disk's surface for interaction therewith. This positioning requiresgenerally a radial displacement, movement, and positioning in relationto the spinning disk. Transducer actuators and positioners areconstructed in several varieties. An earlier version includes a steppingmotor. A later development has concentrated upon voice coil motors; anew development includes a split band in conjunction with a steppingmotor. All of these types of positioners have performed well in the artand are well established accordingly. They are, however, more or lessexpensive and/or heavy, requiring significant power, and havelimitations with respect to speed versus accuracy of positioning.

DESCRIPTION OF THE INVENTION

It is an object of the present invention to provide a new and improvedactuator and positioner for transducers in magnetic disk file systems.

It is a feature of the present invention to provide a magnetic structurewhich includes a core and a coil, riding on parts of the core and beingcoupled to a U-framed member which is linearly guided in direction ofthe coil displacement under prevention of lateral displacement, the coilextending between the legs of the U-frame; the transducers are mountedto extensions from the cross-member of that frame.

In accordance with the preferred embodiment of the invention, a corestructure is to be comprised of a flat, magnetizable bar whose flatsides face two magnets, preferably permanent magnets across two gaps;the magnetic circuit is closed in a manner which shields the transducersfrom stray flux from the gaps, the transducers being mounted upon theU-framed member whose legs carry the coil. A pair of flat springs, eachhaving two legs, is used to mount the U-frame to the base in that oneleg of each spring is anchored to one leg of the U-frame respectively atspaced apart points, while the other leg of each spring is connected tothe base. The junctural ends of the spring legs are interconnected by ahollow frame. The anchor points are aligned in the direction of movementof the U-frame, and they are respectively aligned in perpendiculardirections with the base-connect points of the respective other springleg.

The actuator in accordance with the invention is quite economical, andits construction ensures precise, linear, electrically actuated movementof the transducers with no lateral displacement. The U-frame leg towhich the springs are connected is made stiff, but the other leg may beflexible if thermal compensation of the coil is needed. If not, asecond, similar spring arrangement may be connected to this otherU-frame leg. Torsional stiffness may be enhanced by using E-shapedsprings, each one with a wider center leg being connected, e.g., to thebase, while the respective outer legs are connected to the one U-frameleg, or vice versa.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an actuator in accordance with thepreferred embodiment of the invention;

FIG. 2 is a top view of the actuator shown in FIG. 1

FIGS. 3, 4, and 5 are, respectively, section views taken along lines3--3, 4--4, and 5--5 of FIG. 2;

FIG. 6 is a view similar to FIG. 1, but showing a supplemental feature;

FIG. 7 is a view similar to FIG. 1, but showing a modification; and

FIG. 8 is a section view of a feature applicable to all figures for afour-transducer positioner.

Proceeding now to the detailed description of the drawings, FIGS. 1through 5 illustrate a positioner for a transducer 1, cooperating with aspinning disk 2. The mounting structure for such a transducer head isshown here in a simplified fashion. In reality, more than one transducerhas to be mounted to such an actuator, which is shown in FIG. 8.

The positioner includes a mounting base 10, serving as a stationaryreference. A magnetic structure is mounted on that base, and it includesa flat, magnetizable bar 11 sandwiched in between mounting pieces 12,12b, 12c, and 12d. The pieces 12a and 12b are mounted to base 10, whilepieces 12c and 12d carry a top 13. Parts 12 and 13 as well as base 10are made of magnetically conductive material; so is bar 11.

A pair of permanent magnets 14 and 15 is provided; they are respectivelymounted on base 10 and cover 13 and are in intimate, magneticallyconductive contact therewith. It is convenient and practical to employpermanent magnets in order to obtain stator energization; however, onecould also use electromagnetic energization. The magnetic axes of thesemagnets run transverse to their flat sides so that their faces, facingbar 11 across gaps 16 and 17, are magnetic pole faces. The poles are ofopposite orientation so that the bar 11 is traversed by a uniformmagnetic field.

The device of carriage being positioned is basically a U-shaped frame20, having legs 21 and 22 and a transverse bottom structure or element23. The transducer 1 is shown to be mounted to that bottom structure,particularly to a lateral extension 24 thereof. The bottom traverse 23and the extension 24 together exhibit a T-shaped cross section so thatthe bottom of this U-shaped frame is quite stiff.

Leg 21 is provided with a stiffening ridge 26, but leg 22 has someflexibility. A coil 25 is mounted between the ends of legs 21 and 22.This coil traverses the gaps 16 and 17 respectively between magnets 14and 15 and bar 11. The U-shaped frame with the coil is, thus, a carriageprovided for movement in directions of double arrows 29. This movementis obtained by electrically energizing the coil.

The bar is covered with a thin, axially limited copper coating, servingas a short-circuited, single winding transformer secondary for reducingthe effective inductance of the coil 25. The signal-arise time isreduced by this feature. Additional, rather elastic mounting pieces 18a,18b, 18c, and 18d serve as spacers between the magnets and elements 12.These spacers limit the travel of the coil should it be driven hard,such as in a failure condition. The elastic spacer stops prevent thecoil from coming to an abrupt stop since that may cause the transducerto crash onto the spinning disk, thereby damaging either or both.

Unlike voice coil motor constructions, this core-and-stator constructionexhibits a particularly important feature. The two elements 12b and 12c,together with one end of flat bar 11, shield the transducers and themagnetic disk 2 from any magnetic field emanating from the coil 25 andfrom the permanent magnets. Stray flux toward the transducers and thedisks is not permitted because these elements 12b, 12c, and 11short-circuit such flux as well-defined return path for any magneticfield. Any stray flux laterally escaping from the magnets does notaffect the transducers and the disk.

The U-shaped frame with coil as a whole is mounted as follows. Amounting structure 30 includes a pair of leaf-springs 31 and 32, havinglegs 31a, 31b, and 32a, 32b, and, respectively, juncture portions 31cand 32c. The respective free ends of legs 31b and 32b are fastened tolugs 27a, 27b of U-frame leg 21. The respective free ends of spring legs31a and 32a are secured to the base. The anchoring points for springlegs 31a and 31b are aligned in a direction perpendicular to theextensions of the legs and running in parallel to the direction ofdeflection of the coil and of the U-shaped frame, which is parallel toarrow 29. The anchoring points for spring legs 32a and 32b areanalogously aligned, as specifically shown in FIG. 5. Moreover, theanchoring points for the spring legs 31a and 32a on U-shaped frame leg21 are precisely aligned in a direction parallel to arrow 29; so are theanchoring points of spring legs 31a and 32b on base 10.

The juncture portions 31c and 32c of the two springs are secured to ahollow rectangular frame 33. As a consequence, the anchoring points ofspring arms 31a and 32a on leg 21 move in a single direction, preciselyparallel to arrow 29, whithout lateral displacement. In other words, theU-shaped frame 20 is guided for movement in a perfectly lineardirection. The particular mounting prevents any lateral displacement,though frame 33 will undergo a slight displacement as per double-arrow34. There is no such lateral displacement of frame 20 relative to base10 and to the core structure of this drive. Also, the springs are stiffin the vertical direction being transverse to arrows 34 and 29 so thatthe device is stable in that direction.

The ridge 26 avoids skewing of the spring anchoring points, one aboutthe other, in direction of arrow 34 and , in particular, prevents anyflexing of leg 21 of the U-shaped frame 20. The ridge andtransducer-carrying platform 24 stabilizes the bottom traverse 23,thereby preventing its flexing in a direction parallel to arrow 29 andabout any corner point of the "U." Thus, the transducers (and that isultimately the decisive goal) move on a linear path and in incrementsthat are the precise duplicates of the path of movement and ofincrements of movement of coil 25, there being practically no lateralparasitic movement as between the coil and the transducers.

For reasons of weight, U-shaped frame 20 is made of plastic; so isrectangular frame 33. This means that the two springs 31 and 32 areelectrically isolated from each other provided that at least a portionof the base 10 is also made of insulating material. This fact can beused conveniently for facilitating the current feed to the movable coil.One end of the coil 25 is electrically connected to the free end of leg32a, the other end to leg 31a. Accordingly, feed wires 36a and 36b ofdifferent electrical potential are connected to legs 31b and 32b to,thereby, feed current from a stationary source to the movable coil.

An actuator of the type and construction shown in FIG. 1 was tested inconjunction with a noise generator. The noise signals were applied tothe coil 25 as well as to an input of a spectrum analyzer. Anaccelerometer was placed onto the carriage and U-shaped frame. Itappeared that the amplitude transfer function, specifically as betweenthe amplitude of the signal applied to coil 25 and the resultingmeasured acceleration is practically independent from frequency in therange of from 0 Hz to a few kilohertz. Also, the phase between thesignal applied and the acceleration measured was constant.

The device as described will, of course, exhibit certain very high-orderdeviations from the ideal conditions of strict linearity of movements,simply on account of the flexibility of the springs. However, thesedeviations can be expected to be minute. For example, the assembly31-32-33 is subject to some flexing (torsion), commensurate with arotation about an axis running vertical through frame 33, parallel tothe direction of extension of the spring Also, the flexibility of arm 22introduces a higher-order, parasitic displacement, corresponding to arotation of the "U" of frame 20 about an axis transverse to the plane ofthe U. These two high-order effects are eliminated by structures shownin FIGS. 6 and 7.

The device of FIG. 6 is a supplemented structure of FIGS. 1 to 5, inthat the U-frame arm 22' is not stiff but rigid (ridge 26'), and asecond spring mount 31'-32'-33' is attached to that arm. The resultingsymmetry, thus, ensures the desired parallel motion. This particulardevice is disadvantaged by the fact that any thermal coil expansion orcontraction is not compensated for. This, however, may not be adisadvantage if, in fact, the temperature variations are minute.

FIG. 7 illustrates an assembly in which the two-leg springs of thesuspension are replaced by two three-leg springs 41 and 42. The centerlegs 41a and 42a each are twice as wide as the respective two outer legs41b, 41d, and 42b, 42d. This relation between the width dimensions isnecessary in order to obtain equal conditions for flexing; the frame 43must be displaced by exactly half the distance of the displacement ofthe U-shaped frame 20 relative to a disposition in which all of thesprings are perfectly flat and coplanar.

The assembly as per FIG. 7 shows the free ends of all outer legs to beattached to the stationary structure. This structure includes base 10 aswell as an L-shaped mounting structure 45 extending upward from base 10and across the space above the attachment of spring legs 41a, 42b to theU-frame leg 21. This way, no rotational displacement of the assembly41-42-43 is possible. A torque is provided as a result of oppositedeflections by legs 41a and 41b as well as by legs 42a and 42 b. Thistorque is particularly set up about an axis running parallel to thespring arms; that torque is offset by a torque resulting from thesymmetrical arrangement of oppositely deflected legs 41a and 41d as wellas legs 42a and 42d.

It should be noted that anchoring the middle one of each spring leg tothe U-shaped frame leg is convenient from a construction point of view;but that is not essential. The middle one could be connected to thebase, and the outer ones are connected to the U-shaped frame.

It will be appreciated that, commensurate with the symmetricalduplication feature as shown in FIG. 6, the spring assembly as per FIG.7 can likewise be duplicated to be effective on both of the U-shapedframe arms. In other words, the two constructions as per FIGS. 6 and 7can be combined by duplicating the structure 41, 42, and 43 at the otherarm of the U-shaped frame.

The transducers and their mount have been shown in a somewhat simplifiedfashion in order to concentrate on the mounting structure of thetransducer carriage and positioner proper. FIG. 8 illustrates thepreferred structure in which, in fact, four transducers 1a, 1b, 1c, and1d are positioned with respect to two disks 4 and 5. The bottom 23' ofthe U-shaped frame has, in transverse view, itself a U-shapedconfiguration on account of two mounting platforms 28 (replacing thesingle platform 24) for transducers 1a and 1c. Posts 52 and 53 carryadditional holding platforms 54 and 55 for the transducers 1b and 1d.

The invention is not limited to the embodiments described above; but allchanges and modifications thereof, not constituting departures from thespirit and scope of the invention, are intended to be included.

I claim:
 1. A linear actuator for positioning at least one transducer inone of a plurality of positions and for moving the transducer from oneof the positions to another one thereof, comprising:mounting base means;a flat, bar-shaped, magnetizable core; magnet means for inducing ahomogeneous, magnetic field across the bar, there being gaps between themagnet means and opposite, flat sides of the bar, the magnet furtherincluding magnetic return path means coupled to the flat bar at oppositeends; a coil looping around the flat bar and extending through the gapsfor being movably disposed; frame means of U-shaped configuration,having legs and a transverse base, the coil being fixedly mounted on andbetween the legs, the transducer being mounted on the base of the framemeans; a pair of flat spring means, each of the flat spring means of thepair having a first leg and a second leg, and an integral juncture atone end of each one of the respective first and second leg, each leg ofthe spring means having a free end, the free ends of the first legs ofthe spring means of the pair being secured to one of the legs of theU-shaped frame means, one first leg of one of the spring means beingsecured in a first point of the frame means near said base of the framemeans, the first leg of the other spring means being secured to a secondpoint on the one leg of the U-shaped frame and means spaced from thefirst point; a rectangular frame for interconnecting the junctures ofthe two spring means; and the second legs of the pair of flat springmeans having their respective free ends secured to the mounting basemeans at points in respective alignment with said points in said one legof the U-shaped frame means.
 2. An actuator as in claim 1, the one legof the U-shaped frame means to which said first leg of of the otherspring means is secured, being provided with a stiffening ridge.
 3. Anactuator as in claim 1, said rectangular frame being hollow.
 4. Anactuator as in claim 1, said junctures being spaced by the rectangularframe by a spacing equal to the spacing between said points on the oneof the U-shaped frame means.
 5. An actuator as in claim 2, said otherleg of the U-shaped frame means being relatively flexible.
 6. Anactuator as in claim 1, including a further pair of flat spring meansconfigured as said first-mentioned spring means, there being also afurther rectangular frame connected to said further pair as saidfirst-mentioned rectangular frame is to said first-mentioned springmeans, one free end of each of the further pair being connected to theother leg of the U-shaped frame, other free ends of the further pairbeing connected to the base.
 7. An actuator as in claim 1, each of saidspring means having a third leg, the respective free end of the thirdleg being connected to one of the mounting base means and of theU-shaped frame means, those of the legs of each of the spring meansflexing similarly upon displacement of the coil, being half as wide asthe remaining one.
 8. An actuator as in claim 1, the magnet meansincluding two permanent magnets, facing said flat bar across said gaps.9. An actuator as in claim 1 or 8, including nonmagnetic stop means insaid gaps for limiting the coil displacement.
 10. An actuator as inclaim 1, said spring means as mounted being electrically insulated fromeach other, the coil being electrically connected to the first legs, thesecond legs provided for current feed in.
 11. A linear actuator,comprising:a core structure on a base; a coil magnetically cooperatingwith the core structure to be linearly displaced; frame means ofU-shaped configuration, having legs and a transverse base, the coilbeing mounted on and between the legs, the transducer being mounted onthe base; a pair of flat spring means, each of the flat spring meanshaving a first leg and a second leg and an integral juncture at one endof each one of the respective first and second legs, each leg of thespring means having a free end, the free ends of the first legs of thespring means of the pair being secured to one of the legs of theU-shaped frame means, one first leg of one of the spring means beingsecured in a point near said base, the first leg of the other springmeans being secured to a point on the one leg of the U-shaped framemeans spaced therefrom; a rectangular frame for interconnecting thejunctures of the two spring means; and the second legs having their freeends secured to the base means at points in respective alignment withsaid points in said one U-shaped frame means leg.
 12. A positioner andactuator for at least one transducer, comprising:a mounting base; aU-shaped frame having a bottom traverse and two legs, the transducerbeing mounted to said bottom; a coil mounted on the two legs; core meansmagnetically cooperating with the coil for displacing the coil along aparticular path; and spring means including two U-shaped leaf springs,having their bottoms interconnected by a laterally displaced element,one leg of each U-shaped leaf spring being connected to one leg of theframe, the respective other leg of each leaf spring being connectedrespectively to the mounting base of the frame so that, upondisplacement of the U-shaped frame, the element is displaced by half ofthat displacement.
 13. A positioner and actuator for at least onetransducer, comprising:a mounting base; a U-shaped frame having a bottomtraverse and two legs, the transducer being mounted to said bottom; acoil mounted on the two legs; core means magnetically cooperating withthe coil for displacing the coil along a particular path; and springmeans including two E-shaped leaf springs, each one having two outerlegs connected to the mounting base and one leg of the U-shaped frames,a third, middle one of the legs of each spring being connected to theother one of the mounting base and the said one leg of the U-shapedframe, each middle leg of the two "E's" being twice as wide as therespective outer legs, common elements of each spring beinginterconnected by said laterally displaced element.
 14. A positioner asin claim 12 or 13, the element being a hollow rectangular frame.
 15. Alinear actuator for positioning at least one transducer in one of aplurality of positions and for moving the transducer from one of thepositions to another one thereof, comprising:mounting base means; aflat, bar-shaped, magnetizable core; magnet means for inducing ahomogeneous, magnetic field across the bar, there being gaps between themagnet means and opposite, flat sides of the bar, the magnet meansfurther including magnetic return path means coupled to the flat bar atopposite ends; a coil looping around the flat bar and extending throughthe gaps for being movably disposed; U-shaped frame means having legs,said coil being mounted to said legs, and having a bottom traverse, saidtransducers being mounted to said traverse, said magnetic return pathmeans configured to magnetically shield said transducers from said gaps;a pair of flat spring means, each of the flat spring means having afirst leg and a second leg, and an integral juncture at one end of eachof the respective first and second leg, each leg of the spring meanshaving a free end, the free ends of the first legs of the spring meansof the pair being secured to one of the legs if the U-shaped framemeans, one first leg of one of the spring means being secured to theframe means in a first point near said base of the frame means, thefirst leg of the other spring means being secured to a second point onthe one leg of the U-shaped frame means and from the spaced secondpoint; a rectangular frame for interconnecting the junctures of the twospring means; and the second legs of the pair of flat spring meanshaving their free ends secured to the mounting base means at points inrespective alignment with said first and second points in said one legof the U-shaped frame means.
 16. A linear actuator for positioning atleast one transducer in relation to a spring magnetic disk, comprising:acore structure on a mounting base means; a coil magnetically cooperatingwith the core structure to be linearly displaced; frame means ofU-shaped configuration, having legs and a traverse base, the coil beingfixedly mounted on and between the legs, the transducer being mounted onthe transverse base of the frame means; a pair of flat spring means,each of the flat spring means having a first leg and a second leg, andan integral juncture at one end of each of the respective first andsecond leg, each leg of the spring means having a free end, the freeends of the first legs of the spring means of the pair being secured toone of the legs of the U-shaped frame means, one first leg of one of thespring means being secured in a first point of the frame means near saidbase of the frame means, the first leg of the other spring means beingsecured to a second point on the one leg of the U-shaped frame meansspaced therefrom; a rectangular frame for interconnecting the juncturesof the two spring means; and the second legs having their free endssecured to the mounting base means at points in respective alignmentwith said points in said one leg of the U-shaped frame means.
 17. Alinear actuator as in claim 11 or 16, said core structure comprising:aflat, bar-shaped, magnetizable core; and magnet means for inducing ahomogenic, magnetic field across the bar, there being gaps between themagnet means and opposite, flat sides of the bar, the magnet meansfurther including magnetic return path means coupled to the flat bar atopposite ends.